The present invention relates generally to a new and novel two-piece friction welded motor vehicle axle shaft. More particularly, the present invention relates to a new and novel two-piece friction welded motor vehicle axle shaft which includes an axle portion which is frictionally welded to a flange portion.
Motor vehicle axle shafts are exposed to significant levels of stress, including force and vibration, during operation of the motor vehicle. Torsional overload type failures of motor vehicle axle shafts sometimes occur due to abusive operating conditions. Such failures can cause separation of the wheel and/or the motor vehicle axle shaft from the motor vehicle.
Typical known prior art motor vehicle axle shafts have been fabricated from a single piece of material, typically steel, having a substantially uniform chemical composition throughout the motor vehicle axle shaft. Although the properties in certain portions of the motor vehicle axle shaft can be modified by such material treatment operations as heat treatment or more localized material treatment operations, such as induction hardening, stress relieving, tempering and/or shot peening, the properties which can be obtained are limited by the chemical composition of the material used. This is undesirable because certain portions of the motor vehicle axle shaft are exposed to high contact stresses and thus need additional hardness while other portions of the motor vehicle axle shaft need less hardness but additional ductility. Such a balance of properties is difficult to obtain when using a material having a substantially uniform composition. In addition, specialized material treatment operations can be expensive and time consuming.
Typically, prior art friction welded axle shafts have been used in applications which carry essentially no beaming loads. However, it would be desirable to utilize a two-piece friction welded motor vehicle axle shaft in applications which carry vehicle beaming loads.
A preferred embodiment of the present invention is, therefore, directed to a two-piece friction welded motor vehicle axle shaft which includes an axle portion which is frictionally welded to a flange portion. The flange portion is preferably fabricated from a relatively high carbon steel material, such as SAE 1050 Mod (Mn 0.80-1.10%), to satisfy the hardness requirement for the bearing race and the axle portion is preferably fabricated from a steel barstock material, such as SAE 1038, SAE 1040 or SAE 8630, having a somewhat lower carbon content to maximize its strength and ductility. The friction weld is positioned inboard of the bearing race and, once welded, the two-piece motor vehicle axle shaft is machined to part profile, heat treated and then machined to final print dimensions.
Other advantages and novel features of the present invention will become apparent in the following detailed description of the invention when considered in conjunction with the accompanying drawings.